The present invention relates to a seal device of pneumatic cylinder which satisfies the required tightness of a seal as well as the required lubrication characteristics for a piston movement.
In general, a piston seal, which is applied to maintain different pressures acting on each end of piston, should seal off the gap between a piston and a cylinder inner wall, and at the same time, the sliding friction force caused by the seal should be as small as possible.
Usually the sliding friction force caused by a piston seal has the characteristics of such that it has a large value when a piston is at rest and then decreases abruptly with the increase of piston speed up to a certain critical value, and again increases in proportion to the speed once the piston speed exceeds the critical value.
The problems encountered in the piston movement of a pneumatic cylinder are brought out by the friction characteristics of a piston seal in the range of low piston speed, since the decrease of friction force with the increase of piston speed results in the so called stick-slip phenomenon which prevents the piston for a pneumatic cylinder from smooth moving in low piston speed.